1. Field of the Invention
The invention relates to an electronic ballast for operating a discharge lamp that has electrodes and an electronic transformer for operating a low-volt halogen lamp.
2. Description of the Related Art
The designer of electronic ballasts cannot help thinking first of all of operating any ballast he is to design at the mains frequency, as the mains frequency is available. However, it proves to be the case here that relatively large components have to be selected. A consequence of this is that the ballast is not only expensive, but also that its rates of wear are still relatively great.
Ballast designers have therefore gone over very quickly to using higher frequencies for operating the ballasts, in order to be able to use components of smaller dimensions, with the result that the ballast became smaller and cheaper too. Although it is accepted in this regard that the mains voltage first has to be rectified and a higher-frequency alternating voltage has to be produced from the rectified mains voltage, the advantages described prevail however with regard to the additional expenditure caused thereby. An added advantage is namely the fact that the efficiency of low-pressure discharge lamps increases at higher frequencies.
The range between 20 and 50 kHz was previously regarded as optimum for the choice of starting and operating frequencies for electronic ballasts. This is because the interfering radiation that the ballasts emit on the one hand into the system and that is radiated on the other hand directly into the environment by the antenna effect of the lamp can still be controlled in this range. The permitted emission values are controlled by standards.
The frequency range of 20-50 kHz mentioned has also proved optimal in so far as the dimensions of the discrete components resulting therefrom are still large enough to be suitable for automatic assembly on circuit boards, although a certain stagnation in ballast development has set in due to the stated frequency range.
In contrast to electronic ballasts for gas-discharge lamps, electronic transformers for operating low-volt halogen lamps offer no advantage initially if purely the characteristics of low-volt halogen lamps are considered. However, advantages result from the possibilities yielded by the use of electronic circuits.
Thus, the dependence of the output voltage on the load and the mains voltage can be improved compared with conventional transformers even without expensive controllers. In addition, all the methods that are usual at present for dimming lamps can be used with electronic transformers. Finally, optimum operation can be achieved with the aid of a controlled system, regardless of the external conditions. This is interesting against the background that the luminous flux and life of low-volt halogen lamps are very strongly voltage-dependent.
In the same way as with electronic ballasts, a frequency range between 20 and 50 kHz has proved to be preferred in the development of electronic transformers to operate low volt halogen lamps also. Here, too, a certain stagnation in further development has set in over the course of time.